The present invention relates to a gas purifier apparatus for removing contaminants or impurities from gas streams.
Gas purification to high levels of purity is important in industries such as LED, blue laser, and semiconductor manufacture and the like. Known gas purifiers typically comprise a cylindrical outer housing or canister having an inlet port at one end for receiving a gas to be purified, and an outlet port at the opposite end for exit of purified gas from the housing. The inlet and outlet ports are located co-axially on the central axis of the housing. The housing is filled with a suitable gas purification medium and filter through which the gas passes while traveling in a generally axial direction from the inlet port to the outlet port. The purification medium is of any suitable material or materials for removing the contaminants by absorption or the like.
Retrofit of filters on gas panels with such purifiers to improve gas purity has not been possible in the past due to space limitations on the panel. Panel mounting of gas delivery and purification components is desirable in view of the large space savings and resultant ease of maintenance. A conventional purifier cannot be mounted on such panels in view of the small space or clearance permitted between the inlet and outlet ports and the panel. This means that the housing would have to have a relatively small diameter, and thus a small capacity for purifier medium, so that it could be horizontally mounted on the panel while permitting suitable interconnections to be made between the panel and inlet and outlet ports. Small diameter purifiers are impractical in view of their low flow rates. Small diameter purifiers would also lead to very high pressure drops and very short life times, forcing users to keep toxic and hazardous gases at higher pressures to ensure a sufficient flow rate. The result is more dangerous operating conditions.
A purifier comprising a cylindrical housing with flat end walls and an inlet and outlet port offset from the central axis has been proposed in the past in order to allow sufficient volume capacity for the purifier medium, while permitting it to be fitted in an existing panel mounting arrangement. However, this results in significant xe2x80x9cdead spacexe2x80x9d at the inlet end of the housing where the purifier medium will not be utilized since the gas will not flow through it. Dead space is the volume within a purifier which is not swept by gas flow under normal operating conditions. Regions at the inlet end of the purifier above the offset inlet will typically form such a dead space. Additionally, when the purifier medium needs to be regenerated to remove the absorbed impurities at periodic intervals, it is difficult or impossible to regenerate regions of the chamber adjacent the flat inlet end above the inlet port, which essentially lie in the dead space.
It is an object of the present invention to provide a new and improved gas purification apparatus which can be mounted on a panel to replace existing filters while retaining a sufficient volume of purifier medium for effective removal of impurities from a gas without modifying the panel.
According to the present invention, a gas purification apparatus is provided, which comprises a housing having an internal purification chamber, an inlet end having an inlet port for gas supply to the chamber, and an opposite, outlet end having an outlet port for exit of purified gas from the chamber, the housing being of generally cylindrical shape and having a central axis, an upper portion above the axis, and a lower portion below the axis, and the inlet and outlet ports are offset from the central axis and located in the lower portion of the housing. A suitable purification medium fills at least a major portion of the chamber. The chamber has an internal wall which is cylindrical along part of the length of the housing extending from the outlet end, and which has a rounded or swept, tapering portion extending from the inlet end to the cylindrical part of the internal wall. In an exemplary embodiment, the tapering portion is formed by a part-spherical, spheroidal, or ellipsoidal counter-bore at the inlet end of the chamber. The rounded counter-bore may be formed on a lathe.
The gas purification apparatus in an exemplary embodiment is designed to purify a gas to purity levels of at least 10 ppm, and may provide purity levels better than 1 ppb. The housing material may be stainless steel, nickel or hastalloy. The rounded or swept portion extends from the inlet port up to the cylindrical portion of the bore, and cuts off the corner which would otherwise be present if the cylindrical part extended up to a flat end wall at the inlet, as in the prior art. This ensures that gas entering the chamber at the offset inlet port will flow through the entire volume of purification medium, avoiding any dead space. The offset inlet and outlet port allow the purifier to maintain a large diameter, permitting a larger outlet filter and avoiding the need for dangerously high gas pressures, and permitting the housing to be readily mounted in the limited clearance available on a panel in a gas panel application. The purification medium may be any suitable particulate or molecular purification material, or combination thereof, depending on the nature of the impurities to be removed from the gas.
The swept or rounded inlet portion of the chamber ensures that all portions of the purification medium are used for removal of impurities from the gas, avoiding dead spaces and resultant inefficiency and reduced purification medium lifetime. The purification apparatus can be used with all gases and is regenerable, reducing the cost and problems of hazardous waste disposal. The purification apparatus can be used to replace all existing panel mount filters and purifiers, without any modification of the gas panel. In many cases, purifiers are preferable to filters because they remove molecular contaminants which are impossible for filters to catch. This results in higher purity levels which are advantageous in many manufacturing industries. This invention makes upgrading an existing gas panel from filters to purifiers both easy and inexpensive, since the purifiers can be readily fitted into tight spaces without modification of the existing panel or hardware.